1. Field of the Invention
The present invention relates to a rubber composition, more specifically, it relates to a rubber composition containing a rubber and compounding agents easy to produce and having an excellent wet skid resistance and low rolling resistance.
2. Description of the Related Art
Along with the improvement in performance and improvement in functions of automobiles, demands for the high performance of tires have been increased from year to year. As one of these, there is a strong demand for development of a tire having a strong grip on wet roads, that is, a good wet skid resistance, and providing also a low fuel consumption property. To obtain a low fuel consumption tire, it is necessary to make the tire small in hysteresis loss. However, if the hysteresis loss is reduced, the rolling resistance becomes smaller and the grip is reduced, and therefor, problems arise in driving safety. On the other hand, if the wet skid resistance is improved in order to increase the grip, the rolling resistance, that is, the hysteresis loss, becomes larger and the tire is made poor in fuel consumption property.
Due to this antimonic relationship between the wet skid resistance and the rolling resistance, active researches have been made to satisfy both demands for tire use rubber compositions Various compounding agents for rubber compositions have been reported for rubber compositions providing a large wet skid resistance in spite of a low rolling resistance.
As such compounding agents for improving the dynamic behavior, nitroso-based compounds have been reported. However, nitrosoamine compounds suffer from the problem of a deleterious effect on the human body. At present, the commercial, production thereof has been stopped. (See Kenneth W. Doak et al., Rubber Chem. Technol., 28, 895 (1995), Payne, A. R. et al.; J. Rubber Res. Inst. Malaya, 22, 275 (1969), Walker, L. A. et al., Rubber Age 90, 925 (1962), Patts, K. T. et al., Rubber Chem. Technol., 47, 289 (1974), Daniel F. Graves, Rubber Chem. Technol., 66, 61 (1993).)
Further, dinitroamine-based compounds have been reported as another compounding agents. However, it is reported that, while the improvement in the dynamic behavior as mentioned above is recognized for polyisoprene-based rubber, it is not recognized for butadiene-based rubber such as SBR. (See Yamaguchi, T. et al.; Kautsch. Gummi. Kunstst., 42, 403 (1989).)
As compounding agents exhibiting the above effect on polyisoprene-based rubber and butadiene-based rubber, dialkylamino group-containing sulfur compounds (see Japanese Unexamined Patent Publication (Kokai) No. 9-278942) and aminobenzenesulfonylazide (see Gonzalez, L. et al.; Rubber Chem. Technol., 69, 266 (1996)) have been reported. However, these compounds have defects such as the many production steps and the complicated production process and, in the case of the latter azide compounds, the use, as a synthesis starting material of sodium azide, which has explosiveness and requires caution in handling.
Accordingly, an object of the present invention is to provide a rubber composition containing a rubber and easy-to-produce compounding agents to provide an excellent wet skid resistance and a low rolling resistance.
In accordance with the present invention, there is provided a rubber composition comprising (i) 100 parts by weight of a rubber and (ii) 10 to 180 parts by weight of a composite composed of an oxidative condensate obtained by oxidative condensation of a xcfx80-electron aromatic compound and carbon black.
It must be noted that, as used in the specification and the appended claims, the singular forms xe2x80x9ca,xe2x80x9d xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise.
According to the present invention, by compounding a composite (hereinafter sometimes referred to as the xe2x80x9ccompositexe2x80x9d according to the present invention) composed of (i) an oxidative condensate obtained by oxidative condensation of a xcfx80-electron aromatic compound (hereinafter sometimes referred to as the xe2x80x9coxidative condensatexe2x80x9d according to the present invention) and (ii) carbon black to a rubber, a good wet skid resistance and low rolling resistance can be obtained. Further, the composite of the present invention is a compounding agent having an extremely high industrial applicability, since it is easy to produce.
The xcfx80-electron aromatic compound useable in the present invention is not particularly limited so long as it can form the oxidative condensate of the present invention with an oxidizing agent. The preferable compounds are, for example, aniline, naphthylamine, phenylenediamine, naphthylenediamine, triaminobenzene, triaminonaphthalene, pyrrole, indole, carbazole, thiophene, selenophene, imidazole, furan, benzene, azulene, pyrene, triphenylene, fluorene, benzenedithiol, diphenyldisulfide, phenol, diethynylbenzene, and their derivatives. As the derivatives, for example, compounds having at least one substituent group such as a C1 to C30 alkyl group, C1 to C30 alkoxy group, C2 to C30 alkylenoxide group, sulfonic acid group, C2 to C30 alkylene sulfonic acid group, hydroxyl group, nitro group, amino group, cyano group (di)alkylamino group (i.e., C1 to C30 alkyl group), which are introduced into their aromatic rings may be mentioned. Further, the above compounds may be used alone or in any mixture thereof.
The oxidizing agent usable in the present invention is not particularly limited so long as it can oxidatively condense the xcfx80-electron aromatic compound and form the oxidative condensate of the present invention. The preferable oxidizing agents are, for example, persulfates such as ammonium persulfate and potassium persulfate; trivalent ferric salts such as iron (III) chloride, iron (III) sulfate, and iron (III) nitrate; bivalent copper salts such as copper (II) chloride; permanganates such as sodium permanganate and potassium permanganate; bichromates such as potassium bichromate and sodium bichromate; peroxides such as hydrogen peroxide and peracetic acid; oxygen; ozone; oxidizing enzymes (for example, those illustrated in Liu, W. et al.; J. Am. Chem. Soc. 1999, 121, 71). Further, redox-based initiators such as those composed of divalent ferrous salts and hydrogen peroxide or Lewis acids (e.g., aluminum trichloride, iron trichloride, etc.) and oxidizing agents (e.g., copper salts such as cuprous chloride, cupric chloride, etc.), air (oxygen), etc.) in combination may also be used (for example, those illustrated in Toshima, N. et al.; Chem. Lett. 2000, 1428 or Toshima, N.; Makromol. Chem., Macromol. Symp. 1992, 59, 123). The above oxidizing agents may be used alone or in any mixture thereof. The addition amount of the oxidizing agent is preferably 0.005 to 20, more preferably 0.01 to 10, in terms of molar ratio with respect to the xcfx80-electron aromatic compound (oxidizing agent/xcfx80-electron aromatic compound).
As the oxidative condensate of the present invention, it is possible to use those previously obtained by oxidative condensation of the xcfx80-electron aromatic compound or to perform oxidative condensation after bonding the xcfx80-electron aromatic compound to the carbon black, or to be bonded to the carbon black simultaneously with the oxidative condensation. The oxidative condensate is not particularly limited so long as oxidative condensation of the above xcfx80-electron aromatic compound can be obtained. Preferably, those obtained by oxidative condensates of aniline, pyrrole, thiophene and the derivatives thereof are exemplified.
The xcfx80-conjugated polymer was mentioned as an example of the oxidative condensate of the present invention. This is a polymer having a xcfx80-conjugated system along the polymer chain and is known to exhibit electroconductivity upon doping. Examples of such xcfx80-conjugated polymers are polyaniline, polythiophene, polypyrrole, poly(p-phenylene), poly(p-phenylenevinylene), and derivatives thereof. Among these, those having the formulas given below, that is, polyaniline or its derivatives poly(2-methyl-aniline), polythiophene, polypyrrole, poly(p-phenylene), et c. are preferable in view of the general applicability and superior economicalness. 
wherein, n is 1 to 1000 in each formula.
The oxidative condensate of the present invention is preferably bonded in the composite of the present invention in an amount of 0.01 to 30% by weight, more preferably 0.05 to 25% by weight. By making it at least 0.01% by weight, a greater effect of the present invention is obtained, while even if over 30% by weight, a further effect is difficult to obtain.
The carbon black usable in the present invention is not particularly limited so long as it is a carbon black which is ordinarily compounded into rubber, but carbon black having a nitrogen adsorption specific area (N2SA) of 20 to 200 m2/g is preferable in view of the good processability and reinforcing property when compounded into the rubber. For example, SAF, ISAF, HAF, FEF, and GPF grade carbon black may be mentioned.
The composite of the present invention is composed of the oxidative condensate obtained by oxidative condensation of a xcfx80-electron aromatic compound and carbon black physically or chemically bonded, wherein the oxidative condensate should be present at least on the surface of the composite.
As the production process of the composite of the present invention, for example, (1) the method of treating the surface of carbon black by a solution containing the xcfx80-electron aromatic compound and an inorganic acid and/or organic acid, then treating the surface by a solution containing an oxidizing agent, (2) the method of treating the surface of the carbon black by a solution containing the xcfx80-electron aromatic compound and an inorganic acid and/or organic acid, then treating the surface by a solution containing an oxidizing agent and an inorganic acid and/or organic acid, (3) the method of treating the surface of the carbon black by a solution containing the xcfx80-electron aromatic compound and an inorganic acid and/or organic acid and oxidizing agent, (4) the method of treating the surface of the carbon black by a solution containing an inorganic acid and/or organic acid and oxidizing agent, then treating the surface by a solution containing the xcfx80-electron aromatic compound and an inorganic acid and/or organic acid, (5) the method of treating the surface of the carbon black by a solution containing an inorganic acid and/or organic acid and oxidizing agent, then treating the surface under an atmosphere of the vapor phase of the xcfx80-electron aromatic compound, (6) the method of treating the surface of the carbon black by a solution containing an oxidative condensate, (7) the method of dispersing and mixing carbon black with the oxidative condensate, etc. may be mentioned.
The inorganic acid and/or organic acid usable in the present invention may be any acid, but specifically a protonic acid such as sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, or fluoroboric acid or their salts; carboxylic acids such as acetic acid, formic acid, and benzoic acid and their salts; phenols such as phenol, nitrophenol, and cyanophenol and their salts; organic sulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, p-dodecylbenzenesulfonic acid, alkylnaphthalenesulfonic acid, anthraquinonesulfonic acid, alkylsulfonic acid, dodecylsulfonic acid, camphorsulfonic acid, dioctylsulfosuccinic acid, copper phthalocyanine tetrasulfonic acid, porphyrin tetrasulfonic acid, polystyrenesulfonic acid, polyvinylsulfonic acid, and naphthalenesulfonic acid condensate and their salts; phosphoric acid esters such as propylphosphoric acid ester, butylphosphoric acid ester, hexylphosphoric acid ester, polyethylene oxide dodecyletherphosphoric acid ester, and polyethylene oxide alkyletherphosphoric acid ester and their salts; and sulfuric acid esters such as laurylsulfuric acid ester, cetylsulfuric acid ester, stearylsulfuric acid ester, and laurylethersulfuric acid ester and their salts may be mentioned. Preferably, hydrochloric acid, sulfuric acid, and organic sulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, p-dodecylbenzenesulfonic acid, alkylnaphthalenesulfonic acid, alkylsulfonic acid, dodecylsulfonic acid, camphorsulfonic acid, dioctylsulfosuccinic acid, polystyrenesulfonic acid, polyvinylsulfonic acid, and naphthalenesulfonic acid condensate and their salts may be mentioned. These inorganic acids and/or organic acids may be used alone or in any mixture thereof. The addition amount of the inorganic acid and/or organic acid is preferably 0.001 to 15, more preferably 0.005 to 10, in terms of molar ratio to the xcfx80-electron aromatic compound.
The solvent used when producing the composite of the present invention is not particularly limited so long as it can oxidize and polymerize the xcfx80-electron aromatic compound. Specifically, water; alcohols such as methanol, ethanol, and propanol; ketones such as acetone and methylethylketone; nitrites such as acetonitrile and benzonitrile; N,N-dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone, and propylene carbonate may be mentioned. Preferably, water or a solvent containing water is used.
The reaction temperature of the oxidative condensation reaction is not particularly limited, but is preferably xe2x88x9220 to 400xc2x0 C., more preferably not more than 300xc2x0 C. Even if the reaction temperature is more than 400xc2x0 C., a more improved effect is difficult to obtain.
The composite of the present invention containing an inorganic acid and/or organic acid and produced by the above production processes may be directly compounded into rubber, but it is also possible to process the composite of the present invention to remove the inorganic acid and/or organic acid and then compound it into the rubber. The method of removing the inorganic acid and/or organic acid from the composite of the present invention is not particularly limited. All sorts of known methods are usable. In general, it is sufficient to bring the composite of the present invention including the inorganic acid and/or organic acid into contact with a basic substance. It is possible to form the composite of the present invention, then directly add the basic substance to the reaction mixture containing the composite or isolate the composite of the present invention once, then the basic substance may be applied to the composite of the present invention in a vapor phase or liquid phase. As the basic substance, a primary, secondary, or tertiary alkylamine (for example, mono-, di-, or tri-ethylamine), a hydrazine and its derivatives, an alkali metal hydroxide such as sodium hydroxide and potassium hydroxide, an alkali metal carbonate such as sodium carbonate, potassium carbonate, sodium hydrogencarbonate, or potassium hydrogencarbonate; ammonia; etc. may be mentioned.
The composite of the present invention thus obtained may be dried at room temperature or may be dried under heating. The drying temperature is preferably 10 to 350xc2x0 C., more preferably 25 to 300xc2x0 C.
As the process of production when using a xcfx80-conjugated polymer for the composite of the present invention, there are (1) the method of adding an oxidizing agent to a solution containing a monomer for forming the xcfx80-conjugated polymer and a dopant and having carbon black dispersed therein, (2) the method of adding a monomer for forming the xcfx80-conjugated polymer to a solution containing an oxidizing agent and dopant and having carbon black dispersed therein, (3) the method of adding an oxidizing agent and dopant to a solution containing a monomer for forming the xcfx80-conjugated polymer and having carbon black dispersed therein, (4) the method of adding carbon black to a solution containing a monomer for forming the xcfx80-conjugated polymer, a dopant, and an oxidizing agent, (5) the method of forming a xcfx80-conjugated polymer in a solution containing a monomer for forming the xcfx80-conjugated polymer, a dopant, and an oxidizing agent and treating the surface of carbon black with the solution containing the xcfx80-conjugated polymer, etc. may be mentioned.
The monomer for forming the xcfx80-conjugated polymer is a compound having a conjugated double bond in the molecular structure thereof. Examples of such monomers are aniline, naphthylamine, phenylenediamine, naphthylenediamine, triaminobenzene, triaminonaphthalene, pyrrole, thiophene, furan, benzene, and their derivatives. As the derivatives, for example, compounds having at least one substituent group selected from a C1 to C30 alkyl group, C1 to C30 alkoxy group, C1 to C30 alkylenoxide group, sulfonic acid group, C2 to C30 alkylene sulfonic acid group. Further, the above monomers may be used alone or in any mixture thereof. Other monomers may also be mixed in up to amounts not inhibiting the manifestation of the effect of the present invention.
The oxidizing agent usable in the present invention is not particularly limited so long as it has polymerizing activity with respect to the above monomer. Those mentioned above are also exemplified. The addition amount of the oxidizing agent is preferably 0.005 to 20, more preferably 0.01 to 10, in terms of molar ratio with respect to the monomer (oxidizing agent/monomer).
The dopant used when forming the composite of the present invention is not particularly limited. Any dopant may be used so long as it is able to dope a xcfx80-conjugated polymer compound. Specifically, halogen compounds such as a compound of iodine, bromine, chlorine, or iodine; protonic acids such as sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, or fluoroboric acid; various types of salts of these protonic acids; Lewis acids such as aluminum trichloride, iron trichloride, molybdenum chloride, antimony chloride, arsenic pentafluoride, and antimony pentafluoride; organic acids such as acetic acid, trifluoroacetic acid, benzenesulfonic acid, and p-toluenesulfonic acid; polymer acids such as polyethylenesulfonic acid, polyethylenecarboxylic acid, polyacrylic acid, and polystyrenesulfonic acid; etc. may be mentioned.
Among the dopants, those preferred are protonic acids such as sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, or fluoroboric acid, various types of salts of thereof, carboxylic acids such as acetic acid, formic acid, and benzoic acid and their salts; phenols such as phenol, nitrophenol, and cyanophenol and their salts; organic sulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, p-dodecylbenzenesulfonic acid, alkylnaphthalenesulfonic acid, anthraquinonesulfonic acid, alkylsulfonic acid, dodecylsulfonic acid, camphorsulfonic acid, dioctylsulfosuccinic acid, copper phthalocyanine tetrasulfonic acid, porphyrin tetrasulfonic acid, polystyrenesulfonic acid, polyvinylsulfonic acid, and naphthalenesulfonic acid condensate and their salts; phosphoric acid esters such as propylphosphoric acid ester, butylphosphoric acid ester, hexylphosphoric acid ester, polyethyleneoxide dodecylether phosphoric acid ester, and polyethyleneoxide alkylether phosphoric acid ester and their salts; and sulfuric acid esters such as laurylsulfuric acid ester, cetylsulfuric acid ester, stearylsulfuric acid ester, and laurylethersulfuric acid ester and their salts may be mentioned. Preferably, organic sulfonic acid salts such as benzenesulfonic acid, p-toluenesulfonic acid, p-dodecylbenzenesulfonic acid, alkylnaphthalenesulfonic acid, alkylsulfonic acid, dodecylsulfonic acid, camphorsulfonic acid, dioctylsulfosuccinic acid, polystyrenesulfonic acid, polyvinylsulfonic acid, and naphthalenesulfonic acid condensate and their salts may be mentioned.
Further, these dopants may be used alone or in any mixture thereof. The addition amount of the dopant is preferably 0.001 to 15, more preferably 0.005 to 10, in terms of molar ratio to the monomer (dopant/monomer).
The solvent used when producing the composite of the present invention is not particularly limited so long as it can oxidatively polymerize the monomer, but specifically water; alcohols such as methanol, ethanol, and propanol; ketones such as acetone and methylethylketone; nitrites such as acetonitrile and benzonitrile; N,N-dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone, and propylene carbonate may be preferably used mentioned. More preferably, water or a solvent containing water may be used.
The polymerization temperature during the reaction is not particularly limited, but is preferably xe2x88x9220 to 90xc2x0 C., more preferably not more than 70xc2x0 C. If the polymerization temperature is more than 90xc2x0 C., secondary reactions easily occur and it becomes difficult to form the xcfx80-conjugated polymer compound having the desired structure.
The composite of the present invention containing a dopant and produced by the above production processes may be compounded directly to rubber, but it is also possible to process the composite of the present invention to remove the dopant and then compound it to the rubber. The method of removing the dopant from the composite of the present invention is not particularly limited. All sorts of known methods are possible. In general, it is sufficient to bring the composite of the present invention including the dopant into contact with a basic substance. It is possible to form the composite of the present invention, then directly add the basic substance to the reaction mixture containing the composite or isolate the composite of the present invention once, then the basic substance may be applied to the composite of the present invention in a vapor phase or liquid phase. As the basic substance, a primary, secondary, or tertiary alkylamine (e.g., mono-, di-, or tri-ethylamine), a hydrazine and its derivatives, an alkali metal hydroxide such as sodium hydroxide and potassium hydroxide, an alkali metal carbonate such as sodium carbonate, potassium carbonate, sodium hydrogencarbonate, or potassium hydrogencarbonate; ammonia; etc. may be mentioned.
Further, the composite of the present invention produced without addition of a dopant may also be compounded to the rubber.
The composite of the present invention this obtained may be dried at room temperature or may be dried under heating. The drying temperature is preferably 25 to 350xc2x0 C., more preferably 60 to 300xc2x0 C.
The starting rubber usable in the present invention is at least one rubber selected from natural rubber and a diene-based synthetic rubber. That is, any of natural rubber and the various diene-based synthetic rubbers may be used alone or in any mixture thereof. Examples of the diene-based synthetic rubber, are, polyisoprene rubber, polybutadiene rubber, styrene-butadiene rubber, butyl rubber, chlorobutyl rubber, chloroprene rubber. These rubbers are all illustrations. The present invention is not limited to the above rubbers.
The compounding amount of the composite of the present invention is 10 to 180 parts by weight, preferably 30 to 160 parts by weight, based upon 100 parts by weight of rubber. Further, the composite of the present invention may use a filler ordinarily compounded to rubber. As a suitable filler, silica may be mentioned. When using silica together, the addition amount of the silica is preferably 0 to 120 parts by weight, more preferably 0 to 80 parts by weight, based upon 100 parts by weight of rubber. Further, the ratio by weight of the silica and the composite of the present invention (silica:composite) is preferably from 1:20 to 20:1. The total addition amount of the composite of the present invention is preferably 10 to 180 parts by weight, more preferably 25 to 150 parts by weight, based upon 100 parts by weight of rubber.
Note that when silica is jointly used, it is preferable to use 3 to 20 parts by weight of a silane coupling agent based upon 100 parts by weight of silica. As preferable silane coupling agents, bis(3-triethoxysilylpropyl)tetrasulfide (Si69), bis(3-triethoxysilylpropyl)disulfide (Si75), etc. may be illustrated.
The rubber composition of the present invention may have suitably compounded to it a vulcanization agent, vulcanization accelerator, vulcanization retarder, activating agent, or other curing aid or an additive commonly used as a rubber aid such as an antioxidant, softening agent, plasticizer, or antiaging agent, together with the composite of the present invention.
As the vulcanization agent, sulfur or a sulfur donor vulcanization agent, for example, amine disulfide, a polymer-based polysulfide, or a sulfur/olefin adduct may be mentioned. Sulfur is preferable as the sulfur-based vulcanization agent. Further, it is also possible to use a peroxide as the vulcanization agent. The addition amount of the sulfur-based vulcanization agent is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 10 parts by weight, still more preferably 1 to 6 parts by weight, based upon 100 parts by weight of the rubber. The addition amount of the peroxide is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based upon 100 parts by weight of rubber.
As the vulcanization accelerator, a thiazole type vulcanization accelerator such as dibenzothiazyldisulfide, N-t-butyl-2-benzothiazolylsulfenamide, or N-cyclohexyl-2-benzothiazolylsulfenamide; a thiuram type vulcanization accelerator such as tetramethylthiuramdisulfide; or dithiocarbamic acids, guanidines, thioureas, xantogenic acids, etc. may be mentioned. The vulcanization accelerator is preferably used in an amount of 0.1 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, based upon 100 parts by weight of rubber.
Further, other rubber aids may be used in suitable amounts for the specific application. The suitable amount is 0.1 to 50 parts by weight, based upon 100 parts by weight of the rubber.
The rubber, the composite of the present invention, the other compounding agents, and the rubber aids may be mixed by a conventional mixing method such as mixing using a mixer such as a roll, internal mixer, or Banbury mixer.
The rubber composition according to the aspects of the present invention is not limited to a rubber composition for a tire such as a rubber composition for a tire tread and may be applied to other rubber products as well.